Currently, aircraft are generally equipped with risk area monitoring and warning devices. The risks can be weather-related or relating to collision with obstacles or with the terrain.
Regarding the detection of obstacle or terrain areas, the TAWS system, or “Terrain Awareness & Warning System”, as standalone computer or incorporated with a TCAS (“Terrain Collision Avoidance System”) function, fulfills a terrain collision avoidance monitoring function throughout a flight.
Regarding the detection of potentially hazardous areas and the prediction of how they change in time, an example of an existing environmental data analysis system is the WXR system, the marketing name given to the product developed and marketed by Rockwell Collins (weather radar system). This equipment is used in many aircraft. It comprises a radar antenna, which continually sweeps an angular segment situated in front of the carrier over a parameterizable distance. This equipment analyzes the atmosphere to recover weather data and supply it to the pilot.
Moreover, there are digital weather data models, the information is collected from a certain number of radars on board or located on the ground in real time by a ground station. These digital models can be on board an aircraft in a database and can change over time according to predictions.
In the same way, digital data models of the obstacles and terrain are on board the aircraft.
One aim of these systems is to alert the crew by issuing audible or visual messages on an exceptional approach of the relief or of an obstacle or even in the presence of violent winds or weather conditions that constitute a risk to the safety of the aircraft.
Generally, these hazardous area avoidance systems compare, in real time, a theoretical lateral and/or vertical avoidance trajectory obtained from the capabilities of the aircraft and the data of the potentially hazardous areas.
The calculated trajectory is an extrapolation over a certain duration of the travel of the aircraft in limiting conditions dependent on the performance characteristics of the aircraft.
One drawback of these systems lies in that, on the one hand, the warning of hazardous areas applies only in a near future of a few minutes at most and, on the other hand, that it is not possible to determine in advance potentially hazardous areas in proximity of the trajectory of the aircraft, notably before a flight.
Moreover, on preparing a flight, on the ground, the crew defines a flight plan in the aircraft's computer, which is generally proposed by air traffic control. The flight plan generally comprises a series of points, known in the aeronautical world as “waypoints”, linking a point of departure to a point of arrival. Two successive waypoints generally form a LEG which is a segment or an arc in space. The waypoints are defined by a position in space and comprise information of use to the aircraft such as the altitude and the speed of passage recommended on a passage in proximity to a waypoint or even the predicted passage time.
The flight plans can include waypoints in proximity to hazardous areas or areas including a risk to the safety of the aircraft. It can notably concern mountains, for example, when the latter are situated in proximity to an airport. Moreover, since the weather conditions are random and not always predictable, the flight plans generated by air traffic control do not take into consideration all the weather factors and how they change based on predictions, the updates of the weather database in the aircraft not being systematically carried out.
The American patents U.S. Pat. No. 6,421,603 and U.S. Pat. No. 6,816,780 propose an enhancement on generating a flight plan by taking into account the trajectory to be followed by the aircraft obtained from the flight plan. The solution of these two patents proposes to correlate the trajectory generated from the flight plan of an aircraft and hazard volumes intercepting the trajectory.
This correlation makes it possible to identify the points of the trajectory that include a certain hazard, but it does not make it possible to warn of a hazard close to the trajectory and notably of the warnings that can be issued on the planned passage in proximity to hazard areas.
In these conditions, one drawback of these systems lies in that only the points that present a definite conflict with the terrain or the weather phenomena are taken into account, that is, when the aircraft would already have reached the hazard point.
In these conditions, the aircraft travels a predefined flight plan and the crew has to carry out, as the cases present themselves, corrective maneuvers in real time according to the warnings issued on passage in proximity to hazardous areas that are not identified because they do not strictly intercept the pre-generated trajectory, but do not however respect the required safety margins. In addition to the danger of the proximity of a risk area, some of these warnings can also constitute a nuisance, given their number, the latter originating from passages in proximity to hazardous areas that are not taken into account in generating the initial flight plan.